In one typical application of gas chromatography, a process by which one or more components from a chemical mixture may be separated and identified, a carrier gas, for example, an inert gas such as nitrogen or helium, flows through a tube known as a column. Large size columns may be packed with an inert packing medium coated with an active substance that interacts with components in the chemical mixture being analyzed. Smaller capillary columns are often coated on their inner surface with the active substance. A sample of the chemical mixture to be analyzed is introduced into the column. As the sample is swept through the column with the carrier gas, the different components, each one having a different affinity for the active substance lining the column or coating the packing medium, move through the column at different speeds. Those components having greater affinity for the active substance move more slowly through the column than those having less affinity, and this speed differential results in the components being separated from one another as they pass through and exit the column.
In the foregoing typical application, the carrier gas with the separated components exits the column and passes through a detector. Various types of detectors may be used, including a thermal conductivity detector, a flame ionization detector, electron capture detector, flame photometric detector, photo-ionization detector and a Hall electrolytic conductivity detector. A two dimensional plot of the detector measurements against elution time or volume, known as a chromatogram, may be made, and from the chromatogram or the digital representation thereof the components may be identified.
Introduction of the sample chemical mixture into the column may be effected using a sample inlet assembly. The inlet assembly has a bore in fluid communication with both a source of the carrier gas and the column. An injection port mounted on the inlet assembly is in fluid communication with the bore. The injection port receives a syringe for injecting the sample into the bore. Carrier gas flows from the source through the bore and into the column. The sample is injected into the bore where it is borne by the carrier gas into the column. The sample may initially be in a liquid state, and then vaporized to a gaseous state by the application of heat within the inlet assembly.
The bore has a removable liner made of glass or other substantially inert material to guard against contamination of the sample, which may react with the material comprising the inlet assembly. A seal, for example, an elastomeric O-ring, is positioned between the liner and the bore.